The present invention relates to pressure regulation, and more particularly to a diaphragm-type valve which balances a process pressure against a reference pressure signal.
There are many applications which require a highly precise modulated pressure relief valve for venting fluid when the pressure exceeds a desired dynamic set-point or threshold. An example of a precision valve suitable for such applications is described in U.S. Pat. No. 6,886,591 to Jennings. The '591 patent describes a floating diaphragm relief device which balances vessel, or line pressure, against a reference pressure signal. A simple flexible diaphragm constrained on its periphery separates the reference fluid chamber on one side from a specific seating surface on the other side. This seating surface contains a connection to both the vessel, line or upstream process and vent or downstream environment. The seating surface contains vent holes of varying sizes which, when the diaphragm is not fully seated against them, can communicate from the vessel or line to the vent or lower pressure environment.
Although the valve described in the '591 patent does provide unprecedented performance compared to other forms of back pressure regulation, it is difficult to identify a seat geometry which provides very high performance at both high flow rates and a combination of low flow/low pressure applications.
A coplanar diaphragm constraint is important for low pressures and low flow rates. When the diaphragm constraint surface is coplanar with the plane of vent voids (process surface), this is the lowest stress position for the diaphragm, and also the position with the least chance of wrinkles. The coplanar configuration gives the lowest error for low flow and low pressure applications. However, for many higher flow rate and higher pressure applications, the most optimum design uses a diaphragm constraint which is slightly higher than the plane of the process surface.
Unfortunately, in these existing designs is the seat geometry must be a compromise between the lower pressure and the higher flow rate designs.